In jet engines, it is known to use ejector nozzles to entrain ambient air with engine exhaust gases. The ambient air cools the engine exhaust and improves the overall thrust and performance characteristics during flight. Known systems, such as that described in U.S. Pat. No. 3,409,228, generally include a common nozzle that extends aftward from an engine exhaust source. An ejector inlet located in a nozzle sidewall guides ambient air directly into primary exhaust via an ejector passage connecting the two fluid streams. It is also known to use a nozzle plug assembly or tail cone centrally disposed within the nozzle to control the nozzle duct interior area and shape. Using a plug assembly can greatly increase an engine's propulsive efficiency by allowing the pilot to tailor the engine thrust output and performance characteristics for a specific flight condition.
In recent years it has become important to minimize jet noise, especially during takeoff and landing flight segments. Mixer ejectors, such as "daisy" or lobed designs, provide finger-like mixing lobes at inboard locations along the ejector passage. The lobes work to actively combine ambient air with the engine exhaust. The combined airflow has a lower flow velocity than the average of the separate, uncombined flow velocities. According to current understandings in the art, this lower exhaust exit velocity results in less jet noise.
Because ejectors and mixing components are not needed for all flight conditions, it is known to include additional nozzle parts for stowing the ejectors and mixing components in various nozzle sidewall areas. These additional stowage parts disadvantageously add weight and system complexity to the nozzle. The ejectors, mixing components, and associated parts can also hinder a designer's efforts to create air internal nozzle duct that has a wide range of available shapes for use in a wide range of flight conditions. This is especially problematic when designing for cruise conditions, where pronounced convergent-divergent shapes are required to maximize thrust for given cruise engine settings, mach numbers, and altitudes. Under these circumstances, a desired large duct cross-sectional size may be unattainable due to the space being occupied by an ejector, a mixer, or the various associated components.
Thus, a need exists for a superior aircraft nozzle capable of maintaining engine performance and reducing jet noise through the use of an ejector while additionally providing noise suppression. The ideal nozzle should be configured such that the ejector and mixing structures are present when needed, but not present when not needed. These structures should not interfere with, or limit, the range of available nozzle duct shapes. Preferably, the structures should not add significant additional weight or complexity to the nozzle. The structures should be able to withstand the high temperature, high velocity airflow environment for an entire flight envelope, as well as maintain integrity over the life of an engine installation. The present invention is directed to fulfilling this need.